The drilling of horizontal wells to improve oil and gas recovery and productivity has quickly become one of the most important and promising technology of the oil industry. This is reflected by the considerable number of technical papers published on this subject. Although these papers have been covered a great deal of aspects of horizontal drilling, one important subject remains almost unexplored: the well pressure control.

The scope of this paper is to show important facets of the well control for horizontal wells, especially for deepwater ones, and to highlight some design and operational aspects to make the horizontal drilling safer. One important point analyzed in this paper was the pressure behavior inside a horizontal wellbore during a gas kick removal process. For this analysis, a numerical simulator of a gas kick based on the unsteady state flow of a two-phase mixture (gas and mud) has been developed and used to predict pressure at any point of the wellbore-choke line system. It has also been used to compute and to analyze the kick tolerance during the gas kick circulation process.

Some other relevant points of the well control operation for horizontal wells that differ from those for vertical wells were also investigated.They include:swabbing effect when tripping out of the hole,shut-in pressures and pit gain,drillpipe pressure schedule during the kick removal process,and mud density design.

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